Many local, state and federal agencies require that underground storage tank systems for hazardous materials be secondarily contained. The systems generally include an underground tank, a pump containment sump located on top of the tank, and piping from the containment sump to a ground level dispenser unit. Double walled pipeline systems have recently become popular and in some locales are mandated for underground conveyance of the hazardous material. Such pipeline systems include an inner primary pipeline and an outer secondary pipeline for containing any leakage from the primary pipeline. Inclusion of a leak detection means which monitors for leakage from the inner primary pipeline is a further feature which enhances the systems. In fact, the double walled pipeline systems with leak detection capability for the primary pipeline is a cost effective way of meeting governmental leak detection requirements.
As a part of mandated safety requirements, many ground level dispenser units have pans, sometimes called dispenser sumps, at their base. The primary pipeline from the underground tank is normally under pressure when any dispenser(s) is dispensing fuel to a vehicle. Therefore, it is necessary to have an emergency safety shut-off valve interposed in the primary pipeline to stop the flow of gasoline in an emergency situation. That is, the valve is designed to close when either the dispenser unit is knocked off its mounting or a fire is started. The pan under each dispenser unit provides an area to access the primary pipeline and to install the safety valve. It also provides an area to access and replace the primary pipeline below the valve as well as to access piping above the valve which leads through the dispenser unit. U.S. Pat. No. 5,098,221, FIG. 7 illustrates a typical safety shut-off valve.
Typical dispenser pans result in a large open area under each dispenser unit. The area can collect flammable liquids or vapors which create fire and explosion hazards. The dispenser pans are also prone to fill up with ground water or rain water leaking down into the pan. Some state or local codes prohibit the secondary pipeline of the double walled pipeline system to terminate in an open manner to the interior of the dispenser pan. This is to prevent a collection of liquid or vapors which enters the pan from spreading through the secondary pipe and to the tank containment sump. As readily imagined, this is to prevent the spread of a fire emanating in the dispenser unit to the tank containment sump and possible explosion in the containment sump. The use of dispenser pans is further complicated in that most fire codes require the part of the primary pipeline of the double wall pipeline system which is within the pan to be steel piping or Underwriters Laboratories (UL) fire resistent piping. This means fiberglass and flexible plastic primary piping such as described in U.S. Pat. No. 5,098,221 must terminate underground before entering the dispenser pans.
All connector piping used within the dispenser pan must be fire resistent piping. This piping can be considerably more costly than the flexible piping used to convey the liquid from the storage tank to the dispenser pan. Because of leakage of water, flammable liquids or vapors into the dispenser pan, some fire codes require costly leak detection monitoring to detect leaks into the dispenser pan area. As mentioned above, many codes require the secondary pipeline connected to the pan be sealed so as not to let vapors/liquids from the pan into the secondary pipeline or the tank containment sump. In addition to all these requirements and precautions, dispenser pans are difficult and expensive to install in and under the concrete beneath the dispenser unit. They must be installed in a way to prevent rain or ground water from entering the pan. Many pipe and electrical conduit connections which lead into or from the dispenser pan require field installed seals. Historically, these seals have been problem areas of leakage of ground water into pans. Further heightening the problem is the fact it is costly to repair leaks into a dispenser pan during its operational life.
There are available dispenser units which do not have a dispenser pan. Secondary piping terminates in a liquid-tight sealed manner to a safety valve located at the dispenser's base. However, an associated disadvantage with this type of connection is that access to the primary pipeline is impeded. The primary pipeline is subject to deterioration and it is necessary to periodically remove it from within the secondary pipeline and replace it with new piping. Ideally, this is done without having to disconnect or disturb the secondary pipeline in any manner. It is necessary with known present systems to tamper with the secondary pipeline in any primary pipeline replacement process and this, as can be imagined, creates a whole set of new problems.
There now has been developed a safety shut-off valve assembly which allows for the installation, removal and replacement of a flexible primary pipeline which is connected to a dispenser unit base without unsealing and/or removing the secondary pipeline under the dispenser unit from the safety shut-off valve assembly. The valve assembly eliminates the need for a fire resistent primary pipeline between the flexible primary pipeline and the safety shut-off valve. The safety shut-off valve assembly further eliminates an accumulation of fuel vapors in the dispenser.